A bicycle includes a seat post which is connected with a seat on a top end thereof and the seat post is inserted into the seat tube of the bicycle frame. The seat post can be adjusted along longitudinal axis of the seat tube to set the seat at desired height to meet needs of different users. The adjustment for the seat can be made in two different ways, one of which is to adjust the inclination of the seat relative to the horizontal plane and the other is to adjust the height of the seat relative to the ground. The present invention is developed to the adjustment device for adjustment the height of the bicycle seat.
The conventional methods for adjustment of the seat can be made by mechanical method and by hydraulic method. The mechanical method includes a lever which controls a control unit and the seat post can be adjusted relative to the seat tube by operation of the control unit.
The hydraulic method includes an adjustment unit which includes an adjustment member which is connected to the top end of the seat tube and has an adjustment tube which is connected to the seat tube so as to form an inner space and an outer space between the seat tube and the adjustment member. A path is defined between the adjustment member and the adjustment tube so as to communicate with the inner and outer spaces. An adjustment valve rod movably extends through the path so as to open or close the passages of the adjustment unit. By operation of the adjustment valve rod, the seat post can be set to a desired height.
However, the mechanical method can only provide two-position adjustment to the seat and this may not able to meet requirements for different users. The hydraulic method can set the seat at different heights by adjust the hydraulic fluid between the inner and outer spaces. However, the seat tube and the seat post both require a larger space to accommodate the inner and outer spaces, and the air room and fluid room. The wider and larger seat post and seat tube make the bicycle to be bulky and heavy.
The present invention intends to provide a seat adjustment device which includes a balance unit which is mounted to the seat post and the balance unit provide the device necessary space for the hydraulic fluid and air so that the sizes of the seat post and seat tube do not change.